Python programming

1. Python programming Using the JES picture functions and defining new functions

2. Review • Python – what kind of animal? • JES environment • command area • arithmetic • print command • variables and the assignment statement • Functions • sqrt() • str() • showInformation() • requestInteger()

3. More JES Functions • Some pre-defined functions in JES for picture and sound manipulation • makeEmptyPicture() • makePicture() • makeSound() • show() • play() • pickAFile() • Some of these functions need parameter values:

4. Examples: Manipulating Pictures makeEmptyPicture(width,height) creates a new empty picture show(picture) displays a picture in a separate window >>> pic1 = makeEmptyPicture(200,100) >>> show(pic1) >>> setAllPixelsToAColor(pic1, red) >>> show(pic1) >>> addText(pic1,30,50,“hello") • similarly can add rectangles, lines, etc.

5. More Picture Functions • makePicture(filename) creates and returns a picture object, from the JPEG file at the filename • We’ll learn functions for manipulating pictures later, like getColor(), setColor(), and repaint()

6. Demonstrating picture manipulation with JES >>> >>> print pickAFile() C:\Documents and Settings\mpapalas\Desktop\sample.jpg >>> theFile = "C:\Documents and Settings\mpapalas\Desktop\sample.jpg" >>> makePicture(theFile) Picture, filename C:\Documents and Settings\mpapalas\Desktop\sample.jpg height 1200 width 1600 >>> print makePicture(theFile) Picture, filename C:\Documents and Settings\mpapalas\Desktop\sample.jpg height 1200 width 1600 >>> pic = makePicture(theFile) >>> print pic Picture, filename C:\Documents and Settings\mpapalas\Desktop\sample.jpg height 1200 width 1600 >>> show(pic)

7. Common errors >>> file = pickAFile() >>> pic = makePicture(file) >>> show(file) The error was:sample Name not found globally. A local or global name could not be found. You need to define the function or variable before you try to use it in any way. >>> show(pic) >>> print pic Picture, filename C:\Documents and Settings\mpapalas\Desktop\sample.jpg height 1200 width 1600 Oops!

8. Writing a recipe: Making our own functions def fcnName (input1, input2,...) : block describing what the function should do returnvalue • To make a function, use the command def • Then, the name of the function, and the names of the parameters (input values) between parentheses (“(input1)”, etc), separated by commas. • The body of the recipe is indented (Hint: Use two spaces) • That’s called a block • Optionally, the function can return a value

9. Writing a recipe: Making our own functions • Important: End the line with a colon (“:”) def fcnName (input1, input2,...) : block describing what the function should do returnvalue • To make a function, use the command def • Then, the name of the function, and the names of the input values between parentheses (“(input1)”) • The body of the recipe is indented (Hint: Use two spaces) • That’s called a block • Optionally, the function can return a value

10. Writing a recipe: Making our own functions def fcnName (input1, input2,...) : block describing what the function should do returnvalue • To make a function, use the command def • Then, the name of the function, and the names of the input values between parentheses (“(input1)”) • The body of the recipe is indented (Hint: Use two spaces) • That’s called a block • Optionally, the function can return a value Optional

11. Using a recipe: Invoking our own functions • Once a function has been defined… def fcnName (input1, input2,...) : block describing what the function should do returnvalue … it can be used with any input values of the appropriate type: result1 = fcnName(300, 200)

12. Example: A recipe for displaying picked picture files: defpickAndShow(): theFile = pickAFile() pic = makePicture(theFile) show(pic)

13. A recipe for playing picked sound files def pickAndPlay(): myfile = pickAFile() mysound = makeSound(myfile) play(mysound)

14. Anything complicated is best done in the Program Area Program area - A simple editor for programs • Command area • Interaction with Jython

15. Using the Program Area • Type your program (or cut and paste from the command area) • Save (or Save As) - use .py for file extension • Load Program (click on button between command and program areas) • Before you load it, the program is just a bunch of characters. • Loading encodes it as an executable function • You must Save before Loading • You must Load before you can use your function

16. Making functions the easy way • Get something working by typing commands • Enter the def command. • Copy-paste the right commands into the program area

17. Names for variables and functions can be (nearly)anything! • Must start with a letter (but can contain numerals) • Can’t contain spaces • myPicture is okay but my Picture is not • Be careful not to use command names as your own names • print = 1 won’t work • (Avoid names that appear in the editor pane of JES highlighted in blue or purple) • Case matters • MyPicture is not the same as myPicture or mypicture • Sensible names are sensible • E.g. myPicture is a good name for a picture, but not for a picture file. • x could be a good name for an x-coordinate in a picture, but probably not for anything else

18. Blocking is indicated for you in JES • Statements that are indented the same, are in the same block. • Statements that are in the same block as where the line where the cursor is are enclosed in a blue box.

19. Now what? • After a program with a function definition is loaded, that function can be used either from the command or the program area • Try using your function by typing pickAndShow() in the command area

20. Reading • Sections 2.4, 2.5 from “Introduction to Computing and Programming in Python”

21. Assignment Create a function that… • Pops up a welcome message to the user of your program. (use showInformation()) • Uses an interactive input window to request some form of input from the user and stores it in a variable. For example, ask them to type in their name. (use requestString()) • Pops up another message window where the message contains a word typed in by the user, and also informs them that they will have to select an image file. (use showInformation()) • Gets the image file from the user (use pickAFile()) • Shows the image with whatever the user typed in superimposed over it. (use MakePicture(), addText(), and show()) • Pops up a goodbye message. (use showInformation()) • Be sure to test your function to verify that it works as intended • Show your function to one of your classmates before demonstrating to instructor/TA

22. Example – go() start…Step 1: Pops up a welcome message to the user of your program. (use showInformation())

23. Example – go() requesting input…Step 2: Uses an interactive input window to request some form of input from the user and stores it in a variable. (use requestString())

24. Example – go() using the input…Step 3: Pops up another message window where the message contains a word typed in by the user, and also informs them that they will have to select an image file. (use showInformation())

25. Example – go() selecting an image file…Step 4: Gets the image file from the user (use pickAFile())

26. Example – go() showing image and goodbye message.Step 5: Shows the image with whatever the user typed in superimposed over it. (use MakePicture(), addText(), and show())Step 6: Pops up a goodbye message. (use showInformation())